How Plankton Produce Clouds

How Plankton Produce Clouds
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In many ways, plankton rule the oceans. A typical liter of seawater doesn't contain any fish, but it holds over 1,000,000 of these microscopic marine organisms! Plankton come in two varieties: zooplankton and phytoplankton. The latter are generally recognized as the foundation for the ocean ecosystem, harnessing the energy from sunlight to convert inorganic carbon into nutritive biomass. For all their selfless work, phytoplankton are rewarded by getting eaten by zooplankton, which then are consumed by filter feeders, which then are consumed by predatory fish. Such is life in the ocean.

But phytoplankton affect far more than just ocean life. According to a new study published in Science Advances, phytoplankton hugely contribute to cloud formation, and, in turn, to how much sunlight the Earth absorbs.

Armed with NASA's Terra satellite, researchers primarily based out of the University of Washington and Pacific Northwest National Laboratory fixed their gaze on the Southern Ocean, comprising the southernmost waters of the Pacific, Atlantic, and Indian oceans, and examined the relationship between the density of water droplets in clouds over the region and natural aerosols released into the air by phytoplankton.

Aerosols are solid or liquid particulates suspended in air. They are key to cloud formation because water droplets can condense around them.

The researchers found that phytoplankton release large amounts of aerosols in the form of organic matter and sulfates, and that, on average, these molecules boost cloud formation by 60% over the course of a year! Moreover, when solar radiation is strongest during the summer, cloud formation may even double.

Denser clouds reflect more heat back into space, keeping the Earth cooler. The researchers estimate that plankton reduce the amount of solar energy absorbed by the Southern Ocean by roughly 4 watts per square meter over the course of a year, a small, but noticeable amount.

Scientists previously revealed plankton's possible role in cloud formation back in 2004. A NASA-funded team found that when the sun was too strong, phytoplankton produced a sulfur-based compound that would get broken down by bacteria and filter into the air, potentially to seed clouds above and provide some measure of shade.

Source: D. T. McCoy, S. M. Burrows, R. Wood, D. P. Grosvenor, S. M. Elliott, P.-L. Ma, P. J. Rasch, D. L. Hartmann, Natural aerosols explain seasonal and spatial patterns of Southern Ocean cloud albedo. Sci. Adv. 1, e1500157 (2015).

(Images: NASA via AP, Daniel McCoy / University of Washington)

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